1. Field of the Invention
The present invention is related to the field of telephony, and more specifically to devices, software and methods for implementing a wideband telephony through a network.
2. Description of the Related Art
Conventional telephony uses the Public Switched Telephone Network (PSTN). A direct, dedicated connection is typically established between two subscribers. Such a connection is called circuit switched.
Wideband (WB) telephony is an improvement over common telephony. It encodes a larger portion of the voice frequency range than conventional telephony does, namely from 150 Hz to 7.1 kHz. Since more of the voice sound frequencies are captured, the wider range has resulted in more satisfactory user experience.
A challenge with WB telephony is that it requires a lot of bandwidth to transmit the extra sound frequencies. In fact it requires more bandwidth than is made available by the conventional lines of the PSTN, which is why WB telephony cannot take place via the common PSTN lines.
One way this problem has been addressed is by using special telephone lines, which are also called broadband. These can accommodate the required bandwidth of the WB telephones. The reality remains, however, that broadband lines are not commonly installed.
A recent development is that telephony can be implemented via networks, such as the internet. In this case, the users transmit to each other data packets that are suitable for network transmission, and which encode the voices of the participants.
The advent of network telephony, however, does not solve the problems of WB telephony. This is because the vast majority of users use common modems, such as V.90 dial up modems, to dial into a network gateway via common PSTN lines. While the network itself could transmit packets corresponding to the broadband signal of WB telephony, the transmission bottleneck remains the common modems and telephone lines. The bottleneck occurs because, for a voice signal to be prepared for network transmission, it needs to be packetized. Packetizing involves adding leading headers (also known as leaders) and trailing headers (also known as trailers) to the voice data. Once the leaders and the trailers are added, however, there are more data than can be transmitted via the common telephone lines and modems in real time.